Is HISTFILESIZE behavior different in Yosemite?

For a long time I've used the HISTFILESIZE environmental variable to control the number of lines that get written to my terminal history (the default of 500 is not enough; I set it to 10000). Ever since upgrading to Yosemite, I've been having trouble searching my history for commands I've run in the past. I double checked to make sure the variable is set correctly--it is--but the history is truncated to about 500 lines.

Has the behavior of bash changed with the OS 10.10? I've never had a problem with this before.